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[69.131.148.49]) by smtp.gmail.com with ESMTPSA id 00721157ae682-79a903f3a6bsm70506367b3.16.2026.03.24.02.49.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Mar 2026 02:49:37 -0700 (PDT) Message-ID: <052d27ff-9239-44fa-8604-336de0dc4711@gmail.com> Date: Tue, 24 Mar 2026 05:49:20 -0400 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Where is fuse going? API cleanup, restructuring and more To: Gao Xiang , Christian Brauner , Jan Kara Cc: "Darrick J. Wong" , Miklos Szeredi , linux-fsdevel@vger.kernel.org, Joanne Koong , John Groves , Bernd Schubert , Amir Goldstein , Luis Henriques , Horst Birthelmer , Gao Xiang , lsf-pc@lists.linux-foundation.org References: <361d312b-9706-45ca-8943-b655a75c765b@gmail.com> <390cd031-742b-4f1b-99c4-8ee41a259744@linux.alibaba.com> <72eaaed1-24a0-4c98-a7c0-ea249d541f2d@linux.alibaba.com> <9af9ad0e-8070-4aaa-9f64-7d72074bd948@linux.alibaba.com> <68116ee5-b1f7-484b-a520-7dc5aefd7738@linux.alibaba.com> <2gyfmxfnnxrglpzb7kz63xbve5vnosl6gi54c3umgrpwbjr4og@lz4e2ptqanfe> <20260324-hilfen-reibung-9783005d5d0f@brauner> Content-Language: en-US From: Demi Marie Obenour Autocrypt: addr=demiobenour@gmail.com; keydata= xsFNBFp+A0oBEADffj6anl9/BHhUSxGTICeVl2tob7hPDdhHNgPR4C8xlYt5q49yB+l2nipd aq+4Gk6FZfqC825TKl7eRpUjMriwle4r3R0ydSIGcy4M6eb0IcxmuPYfbWpr/si88QKgyGSV Z7GeNW1UnzTdhYHuFlk8dBSmB1fzhEYEk0RcJqg4AKoq6/3/UorR+FaSuVwT7rqzGrTlscnT DlPWgRzrQ3jssesI7sZLm82E3pJSgaUoCdCOlL7MMPCJwI8JpPlBedRpe9tfVyfu3euTPLPx wcV3L/cfWPGSL4PofBtB8NUU6QwYiQ9Hzx4xOyn67zW73/G0Q2vPPRst8LBDqlxLjbtx/WLR 6h3nBc3eyuZ+q62HS1pJ5EvUT1vjyJ1ySrqtUXWQ4XlZyoEFUfpJxJoN0A9HCxmHGVckzTRl 5FMWo8TCniHynNXsBtDQbabt7aNEOaAJdE7to0AH3T/Bvwzcp0ZJtBk0EM6YeMLtotUut7h2 Bkg1b//r6bTBswMBXVJ5H44Qf0+eKeUg7whSC9qpYOzzrm7+0r9F5u3qF8ZTx55TJc2g656C 9a1P1MYVysLvkLvS4H+crmxA/i08Tc1h+x9RRvqba4lSzZ6/Tmt60DPM5Sc4R0nSm9BBff0N m0bSNRS8InXdO1Aq3362QKX2NOwcL5YaStwODNyZUqF7izjK4QARAQABzTxEZW1pIE1hcmll IE9iZW5vdXIgKGxvdmVyIG9mIGNvZGluZykgPGRlbWlvYmVub3VyQGdtYWlsLmNvbT7CwXgE EwECACIFAlp+A0oCGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJELKItV//nCLBhr8Q AK/xrb4wyi71xII2hkFBpT59ObLN+32FQT7R3lbZRjVFjc6yMUjOb1H/hJVxx+yo5gsSj5LS 9AwggioUSrcUKldfA/PKKai2mzTlUDxTcF3vKx6iMXKA6AqwAw4B57ZEJoMM6egm57TV19kz PMc879NV2nc6+elaKl+/kbVeD3qvBuEwsTe2Do3HAAdrfUG/j9erwIk6gha/Hp9yZlCnPTX+ VK+xifQqt8RtMqS5R/S8z0msJMI/ajNU03kFjOpqrYziv6OZLJ5cuKb3bZU5aoaRQRDzkFIR 6aqtFLTohTo20QywXwRa39uFaOT/0YMpNyel0kdOszFOykTEGI2u+kja35g9TkH90kkBTG+a EWttIht0Hy6YFmwjcAxisSakBuHnHuMSOiyRQLu43ej2+mDWgItLZ48Mu0C3IG1seeQDjEYP tqvyZ6bGkf2Vj+L6wLoLLIhRZxQOedqArIk/Sb2SzQYuxN44IDRt+3ZcDqsPppoKcxSyd1Ny 2tpvjYJXlfKmOYLhTWs8nwlAlSHX/c/jz/ywwf7eSvGknToo1Y0VpRtoxMaKW1nvH0OeCSVJ itfRP7YbiRVc2aNqWPCSgtqHAuVraBRbAFLKh9d2rKFB3BmynTUpc1BQLJP8+D5oNyb8Ts4x Xd3iV/uD8JLGJfYZIR7oGWFLP4uZ3tkneDfYzsFNBFp+A0oBEAC9ynZI9LU+uJkMeEJeJyQ/ 8VFkCJQPQZEsIGzOTlPnwvVna0AS86n2Z+rK7R/usYs5iJCZ55/JISWd8xD57ue0eB47bcJv VqGlObI2DEG8TwaW0O0duRhDgzMEL4t1KdRAepIESBEA/iPpI4gfUbVEIEQuqdqQyO4GAe+M kD0Hy5JH/0qgFmbaSegNTdQg5iqYjRZ3ttiswalql1/iSyv1WYeC1OAs+2BLOAT2NEggSiVO txEfgewsQtCWi8H1SoirakIfo45Hz0tk/Ad9ZWh2PvOGt97Ka85o4TLJxgJJqGEnqcFUZnJJ riwoaRIS8N2C8/nEM53jb1sH0gYddMU3QxY7dYNLIUrRKQeNkF30dK7V6JRH7pleRlf+wQcN fRAIUrNlatj9TxwivQrKnC9aIFFHEy/0mAgtrQShcMRmMgVlRoOA5B8RTulRLCmkafvwuhs6 dCxN0GNAORIVVFxjx9Vn7OqYPgwiofZ6SbEl0hgPyWBQvE85klFLZLoj7p+joDY1XNQztmfA rnJ9x+YV4igjWImINAZSlmEcYtd+xy3Li/8oeYDAqrsnrOjb+WvGhCykJk4urBog2LNtcyCj kTs7F+WeXGUo0NDhbd3Z6AyFfqeF7uJ3D5hlpX2nI9no/ugPrrTVoVZAgrrnNz0iZG2DVx46 x913pVKHl5mlYQARAQABwsFfBBgBAgAJBQJafgNKAhsMAAoJELKItV//nCLBwNIP/AiIHE8b oIqReFQyaMzxq6lE4YZCZNj65B/nkDOvodSiwfwjjVVE2V3iEzxMHbgyTCGA67+Bo/d5aQGj gn0TPtsGzelyQHipaUzEyrsceUGWYoKXYyVWKEfyh0cDfnd9diAm3VeNqchtcMpoehETH8fr RHnJdBcjf112PzQSdKC6kqU0Q196c4Vp5HDOQfNiDnTf7gZSj0BraHOByy9LEDCLhQiCmr+2 E0rW4tBtDAn2HkT9uf32ZGqJCn1O+2uVfFhGu6vPE5qkqrbSE8TG+03H8ecU2q50zgHWPdHM OBvy3EhzfAh2VmOSTcRK+tSUe/u3wdLRDPwv/DTzGI36Kgky9MsDC5gpIwNbOJP2G/q1wT1o Gkw4IXfWv2ufWiXqJ+k7HEi2N1sree7Dy9KBCqb+ca1vFhYPDJfhP75I/VnzHVssZ/rYZ9+5 1yDoUABoNdJNSGUYl+Yh9Pw9pE3Kt4EFzUlFZWbE4xKL/NPno+z4J9aWemLLszcYz/u3XnbO vUSQHSrmfOzX3cV4yfmjM5lewgSstoxGyTx2M8enslgdXhPthZlDnTnOT+C+OTsh8+m5tos8 HQjaPM01MKBiAqdPgksm1wu2DrrwUi6ChRVTUBcj6+/9IJ81H2P2gJk3Ls3AVIxIffLoY34E +MYSfkEjBz0E8CLOcAw7JIwAaeBT In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------0p99z1qlkyfZ3vhfDZEUo2g4" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --------------0p99z1qlkyfZ3vhfDZEUo2g4 Content-Type: multipart/mixed; boundary="------------uNjJpRa3vws8Fs0jCvmSk8xa"; protected-headers="v1" Message-ID: <052d27ff-9239-44fa-8604-336de0dc4711@gmail.com> Date: Tue, 24 Mar 2026 05:49:20 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Where is fuse going? API cleanup, restructuring and more To: Gao Xiang , Christian Brauner , Jan Kara Cc: "Darrick J. Wong" , Miklos Szeredi , linux-fsdevel@vger.kernel.org, Joanne Koong , John Groves , Bernd Schubert , Amir Goldstein , Luis Henriques , Horst Birthelmer , Gao Xiang , lsf-pc@lists.linux-foundation.org References: <361d312b-9706-45ca-8943-b655a75c765b@gmail.com> <390cd031-742b-4f1b-99c4-8ee41a259744@linux.alibaba.com> <72eaaed1-24a0-4c98-a7c0-ea249d541f2d@linux.alibaba.com> <9af9ad0e-8070-4aaa-9f64-7d72074bd948@linux.alibaba.com> <68116ee5-b1f7-484b-a520-7dc5aefd7738@linux.alibaba.com> <2gyfmxfnnxrglpzb7kz63xbve5vnosl6gi54c3umgrpwbjr4og@lz4e2ptqanfe> <20260324-hilfen-reibung-9783005d5d0f@brauner> Content-Language: en-US From: Demi Marie Obenour Autocrypt: addr=demiobenour@gmail.com; keydata= xsFNBFp+A0oBEADffj6anl9/BHhUSxGTICeVl2tob7hPDdhHNgPR4C8xlYt5q49yB+l2nipd aq+4Gk6FZfqC825TKl7eRpUjMriwle4r3R0ydSIGcy4M6eb0IcxmuPYfbWpr/si88QKgyGSV Z7GeNW1UnzTdhYHuFlk8dBSmB1fzhEYEk0RcJqg4AKoq6/3/UorR+FaSuVwT7rqzGrTlscnT DlPWgRzrQ3jssesI7sZLm82E3pJSgaUoCdCOlL7MMPCJwI8JpPlBedRpe9tfVyfu3euTPLPx wcV3L/cfWPGSL4PofBtB8NUU6QwYiQ9Hzx4xOyn67zW73/G0Q2vPPRst8LBDqlxLjbtx/WLR 6h3nBc3eyuZ+q62HS1pJ5EvUT1vjyJ1ySrqtUXWQ4XlZyoEFUfpJxJoN0A9HCxmHGVckzTRl 5FMWo8TCniHynNXsBtDQbabt7aNEOaAJdE7to0AH3T/Bvwzcp0ZJtBk0EM6YeMLtotUut7h2 Bkg1b//r6bTBswMBXVJ5H44Qf0+eKeUg7whSC9qpYOzzrm7+0r9F5u3qF8ZTx55TJc2g656C 9a1P1MYVysLvkLvS4H+crmxA/i08Tc1h+x9RRvqba4lSzZ6/Tmt60DPM5Sc4R0nSm9BBff0N m0bSNRS8InXdO1Aq3362QKX2NOwcL5YaStwODNyZUqF7izjK4QARAQABzTxEZW1pIE1hcmll IE9iZW5vdXIgKGxvdmVyIG9mIGNvZGluZykgPGRlbWlvYmVub3VyQGdtYWlsLmNvbT7CwXgE EwECACIFAlp+A0oCGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJELKItV//nCLBhr8Q AK/xrb4wyi71xII2hkFBpT59ObLN+32FQT7R3lbZRjVFjc6yMUjOb1H/hJVxx+yo5gsSj5LS 9AwggioUSrcUKldfA/PKKai2mzTlUDxTcF3vKx6iMXKA6AqwAw4B57ZEJoMM6egm57TV19kz PMc879NV2nc6+elaKl+/kbVeD3qvBuEwsTe2Do3HAAdrfUG/j9erwIk6gha/Hp9yZlCnPTX+ VK+xifQqt8RtMqS5R/S8z0msJMI/ajNU03kFjOpqrYziv6OZLJ5cuKb3bZU5aoaRQRDzkFIR 6aqtFLTohTo20QywXwRa39uFaOT/0YMpNyel0kdOszFOykTEGI2u+kja35g9TkH90kkBTG+a EWttIht0Hy6YFmwjcAxisSakBuHnHuMSOiyRQLu43ej2+mDWgItLZ48Mu0C3IG1seeQDjEYP tqvyZ6bGkf2Vj+L6wLoLLIhRZxQOedqArIk/Sb2SzQYuxN44IDRt+3ZcDqsPppoKcxSyd1Ny 2tpvjYJXlfKmOYLhTWs8nwlAlSHX/c/jz/ywwf7eSvGknToo1Y0VpRtoxMaKW1nvH0OeCSVJ itfRP7YbiRVc2aNqWPCSgtqHAuVraBRbAFLKh9d2rKFB3BmynTUpc1BQLJP8+D5oNyb8Ts4x Xd3iV/uD8JLGJfYZIR7oGWFLP4uZ3tkneDfYzsFNBFp+A0oBEAC9ynZI9LU+uJkMeEJeJyQ/ 8VFkCJQPQZEsIGzOTlPnwvVna0AS86n2Z+rK7R/usYs5iJCZ55/JISWd8xD57ue0eB47bcJv VqGlObI2DEG8TwaW0O0duRhDgzMEL4t1KdRAepIESBEA/iPpI4gfUbVEIEQuqdqQyO4GAe+M kD0Hy5JH/0qgFmbaSegNTdQg5iqYjRZ3ttiswalql1/iSyv1WYeC1OAs+2BLOAT2NEggSiVO txEfgewsQtCWi8H1SoirakIfo45Hz0tk/Ad9ZWh2PvOGt97Ka85o4TLJxgJJqGEnqcFUZnJJ riwoaRIS8N2C8/nEM53jb1sH0gYddMU3QxY7dYNLIUrRKQeNkF30dK7V6JRH7pleRlf+wQcN fRAIUrNlatj9TxwivQrKnC9aIFFHEy/0mAgtrQShcMRmMgVlRoOA5B8RTulRLCmkafvwuhs6 dCxN0GNAORIVVFxjx9Vn7OqYPgwiofZ6SbEl0hgPyWBQvE85klFLZLoj7p+joDY1XNQztmfA rnJ9x+YV4igjWImINAZSlmEcYtd+xy3Li/8oeYDAqrsnrOjb+WvGhCykJk4urBog2LNtcyCj kTs7F+WeXGUo0NDhbd3Z6AyFfqeF7uJ3D5hlpX2nI9no/ugPrrTVoVZAgrrnNz0iZG2DVx46 x913pVKHl5mlYQARAQABwsFfBBgBAgAJBQJafgNKAhsMAAoJELKItV//nCLBwNIP/AiIHE8b oIqReFQyaMzxq6lE4YZCZNj65B/nkDOvodSiwfwjjVVE2V3iEzxMHbgyTCGA67+Bo/d5aQGj gn0TPtsGzelyQHipaUzEyrsceUGWYoKXYyVWKEfyh0cDfnd9diAm3VeNqchtcMpoehETH8fr RHnJdBcjf112PzQSdKC6kqU0Q196c4Vp5HDOQfNiDnTf7gZSj0BraHOByy9LEDCLhQiCmr+2 E0rW4tBtDAn2HkT9uf32ZGqJCn1O+2uVfFhGu6vPE5qkqrbSE8TG+03H8ecU2q50zgHWPdHM OBvy3EhzfAh2VmOSTcRK+tSUe/u3wdLRDPwv/DTzGI36Kgky9MsDC5gpIwNbOJP2G/q1wT1o Gkw4IXfWv2ufWiXqJ+k7HEi2N1sree7Dy9KBCqb+ca1vFhYPDJfhP75I/VnzHVssZ/rYZ9+5 1yDoUABoNdJNSGUYl+Yh9Pw9pE3Kt4EFzUlFZWbE4xKL/NPno+z4J9aWemLLszcYz/u3XnbO vUSQHSrmfOzX3cV4yfmjM5lewgSstoxGyTx2M8enslgdXhPthZlDnTnOT+C+OTsh8+m5tos8 HQjaPM01MKBiAqdPgksm1wu2DrrwUi6ChRVTUBcj6+/9IJ81H2P2gJk3Ls3AVIxIffLoY34E +MYSfkEjBz0E8CLOcAw7JIwAaeBT In-Reply-To: --------------uNjJpRa3vws8Fs0jCvmSk8xa Content-Type: multipart/mixed; boundary="------------JNjYXEKadNMHapBiHDAyAjcc" --------------JNjYXEKadNMHapBiHDAyAjcc Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 3/24/26 05:30, Gao Xiang wrote: > Hi Christian, >=20 > On 2026/3/24 16:48, Christian Brauner wrote: >> On Mon, Mar 23, 2026 at 03:47:24PM +0100, Jan Kara wrote: >>> On Mon 23-03-26 22:36:46, Gao Xiang wrote: >>>> On 2026/3/23 22:13, Jan Kara wrote: >>>>>>> think that is the corner cases if you don't claim the >>>>>>> limitation of FUSE approaches. >>>>>>> >>>>>>> If none expects that, that is absolute be fine, as I said, >>>>>>> it provides strong isolation and stability, but I really >>>>>>> suspect this approach could be abused to mount totally >>>>>>> untrusted remote filesystems (Actually as I said, some >>>>>>> business of ours already did: fetching EXT4 filesystems >>>>>>> with unknown status and mount without fscking, that is >>>>>>> really disappointing.) >>>>> >>>>> Yes, someone downloading untrusted ext4 image, mounting in read-wri= te and >>>>> using it for sensitive application, that falls to "insane" category= for me >>>>> :) We agree on that. And I agree that depending on the application = using >>>>> FUSE to access such filesystem needn't be safe enough and immutable= fs + >>>>> overlayfs writeable layer may provide better guarantees about fs be= havior. >>>> >>>> That is my overall goal, I just want to make it clear >>>> the difference out of write isolation, but of course, >>>> "secure" or not is relative, and according to the >>>> system design. >>>> >>>> If isolation and system stability are enough for >>>> a system and can be called "secure", yes, they are >>>> both the same in such aspects. >>>> >>>>> I would still consider such design highly suspicious but without mo= re >>>>> detailed knowledge about the application I cannot say it's outright= broken >>>>> :). >>>> >>>> What do you mean "such design"? "Writable untrusted >>>> remote EXT4 images mounting on the host"? Really, we have >>>> such applications for containers for many years but I don't >>>> want to name it here, but I'm totally exhaused by such >>>> usage (since I explained many many times, and they even >>>> never bother with LWN.net) and the internal team. >>> >>> By "such design" I meant generally the concept that you fetch filesys= tem >>> images (regardless whether ext4 or some other type) from untrusted so= urce. >>> Unless you do cryptographical verification of the data, you never kno= w what >>> kind of garbage your application is processing which is always invita= tion >>> for nasty exploits and bugs... >> >> If this is another 500 mail discussion about FS_USERNS_MOUNT on >> block-backed filesystems then my verdict still stands that the only >> condition under which I will let the VFS allow this if the underlying >> device is signed and dm-verity protected. The kernel will continue to >> refuse unprivileged policy in general and specifically based on qualit= y >> or implementation of the underlying filesystem driver. >=20 >=20 > First, if block devices are your concern, fine, how about > allowing it if EROFS file-backed mounts and S_IMMUTABLE > for underlay files is set, and refuse any block device > mounts. >=20 > If the issue is "you don't know how to define the quality > or implementation of the underlying filesystem drivers", > you could list your detailed concerns (I think at least > people have trust to the individual filesystem > maintainers' judgements), otherwise there will be endless > new sets of new immutable filesystems for this requirement > (previously, composefs , puzzlefs, and tarfs are all for > this; I admit I didn't get the point of FS_USERNS_MOUNT > at that time of 2023; but know I also think FS_USERNS_MOUNT > is a strong requirement for DinD for example), because that > idea should be sensible according to Darrick and Jan's > reply, and I think more people will agree with that. >=20 > And another idea is that you still could return arbitary > metadata with immutable FUSE fses and let users get > garbage (meta)data, and FUSE already allows FS_USERNS_MOUNT, > and if user and mount namespaces are isolated, why bothering > it? >=20 > I just hope know why? And as you may notice, > "Demi Marie Obenour wrote:" >=20 >> The only exceptions are if the filesystem is incredibly simple >> or formal methods are used, and neither is the case for existing >> filesystems in the Linux kernel.=20 >=20 > I still strong disagree with that judgement, a minimal EROFS > can build an image with superblock, dirs, and files with > xattrs in a 4k-size image; and 4k image should be enough for > fuzzing; also the in-core EROFS format even never allocates > any extra buffers, which is much simplar than FUSE. >=20 > In brief, so how to meet your requirement? >=20 > Thanks, > Gao Xiang Rewriting the code in Rust would dramatically reduce the attack surface when it comes to memory corruption. That's a lot to ask, though, and a lot of work. --=20 Sincerely, Demi Marie Obenour (she/her/hers) --------------JNjYXEKadNMHapBiHDAyAjcc Content-Type: application/pgp-keys; name="OpenPGP_0xB288B55FFF9C22C1.asc" Content-Disposition: attachment; filename="OpenPGP_0xB288B55FFF9C22C1.asc" Content-Description: OpenPGP public key Content-Transfer-Encoding: quoted-printable -----BEGIN PGP PUBLIC KEY BLOCK----- xsFNBFp+A0oBEADffj6anl9/BHhUSxGTICeVl2tob7hPDdhHNgPR4C8xlYt5q49y B+l2nipdaq+4Gk6FZfqC825TKl7eRpUjMriwle4r3R0ydSIGcy4M6eb0IcxmuPYf bWpr/si88QKgyGSVZ7GeNW1UnzTdhYHuFlk8dBSmB1fzhEYEk0RcJqg4AKoq6/3/ UorR+FaSuVwT7rqzGrTlscnTDlPWgRzrQ3jssesI7sZLm82E3pJSgaUoCdCOlL7M MPCJwI8JpPlBedRpe9tfVyfu3euTPLPxwcV3L/cfWPGSL4PofBtB8NUU6QwYiQ9H zx4xOyn67zW73/G0Q2vPPRst8LBDqlxLjbtx/WLR6h3nBc3eyuZ+q62HS1pJ5EvU T1vjyJ1ySrqtUXWQ4XlZyoEFUfpJxJoN0A9HCxmHGVckzTRl5FMWo8TCniHynNXs BtDQbabt7aNEOaAJdE7to0AH3T/Bvwzcp0ZJtBk0EM6YeMLtotUut7h2Bkg1b//r 6bTBswMBXVJ5H44Qf0+eKeUg7whSC9qpYOzzrm7+0r9F5u3qF8ZTx55TJc2g656C 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